Approaches for the Design of Foundations for Offshore Wind Turbines

The design of foundations for offshore wind turbines is still a challenging engineering task. Design rules are not always settled in national standards and especially tasks like the design against cyclic loading remain a field where results of scientific research are immediately implemented in practical design approaches. The PISA project demonstrated, that even the static design of monopiles can be improved by validating new design approaches and implementing them in design tools. This paper compares different approaches for the static and cyclic design of foundations for offshore wind turbines, including new approaches like PISA, SOLDYN and TANDEM, as far as available. Focus is laid on the validation process of a cyclic approach, based on the high cycle accumulation (HCA) model. The main results of this validation on monopiles and shallow foundations in different scales are discussed. The HCA model showed to be very well suited to simulate and predict the cyclic soil structure interaction processes of foundations for offshore wind turbines. Effects like the accumulation of deformations or the redistribution of stresses and internal forces induced by a cyclic loading on monopiles or shallow foundations are well reproduced by the HCA model. This is demonstrated based on a comparison of results from model tests and in situ tests with numerical predictions. Furthermore, the results of these studies on the HCA model are set in relation to the approaches from other research groups. The outcome of the PISA project for the static design of monopiles is shown and reviewed based on the own results of numerical simulations.